Tubes for medical applications have traditionally been made of glass. Glass is advantageous because of its clarity, recycleability and freedom from any morphological changes, but suffers from the severe disadvantage of breakability. In recent years, plastic has come to the fore as a replacement for glass in fabrication of medical tubes. Plastic provides the advantages of lower breakage than glass, less weight in shipment and easier disposal by incineration.
For small medical tubes (10 ml or less), polystyrene (PS) has conventionally been the plastic of choice because of its ease of injection molding and high clarity. It does, however, shatter easily due to inherent brittleness, a disadvantage which is magnified when fabricated into tubes of larger capacity. For this reason, larger tubes have conventionally been made of styrene-butadiene copolymer (S-Bu), styrene-butadiene-styrene terpolymer (S-Bu-S), and crosslinked blends of S-Bu and S-Bu-S or other elastomers. Such compositions are disclosed in U.S. Pat. No. 4,371,663 and in U.S. Pat. No. 5,248,729.
While improved polystyrene compositions have been disclosed, there is yet a need in the art for still better compositions combining the excellent clarity of polystyrene with the toughness of styrene-butadiene elastomers. This invention is directed to fulfulling this need.